1. Field of the Invention
This invention concerns improvements in and relating to ion detection, particularly, but not exclusively to the detection of ions produced by the passage of alpha particles through a medium, such as a gas.
2. Present State of the Art
Alpha particles are only directly detectable a short distance from their source. As a consequence of this longer range detection techniques have been developed based on the ions produced in the air during the passage of alpha particles. These ions are electrostatically attracted towards a detection location and/or forced towards such a detection location by the flow of air within the apparatus. Once within the detector unit, the electric field existing between electrodes and/or between electrodes and the apparatus attracts ions of one polarity. The current arising can subsequently be measured and the level of alpha contamination present be determined from this current.
The number of ions produced is relatively low and as a consequence the currents arising are relatively low. Because of the low signal level, these signals are prone to interference from background noise and are also close to the practical level detectable in certain circumstances. It is therefore desirable to maximise the number of ions actually detected by the apparatus so as to obtain the strongest signal possible.